I don't know... I don't have kids, so it's not really something I can fairly comment on. I can just guess/think from what I feel on the matter from a teacher's perspective, and knowing children like I do. I kind of think that 15-16 is too young for someone to make that decision. Certainly, many will make their own choices anyhow, but I think to let them freely do it (or encourage him) like it seems some might (and some are encouraging in the thread), is quite contrary to how I would handle it. Cigars are a great thing, and maybe since I'm only late to the party (I've only really picked it up as a hobby in the last two years, with having never really smoked prior) my concepts are different. The concept that he's sneaking around it, and doing it with friends would lead me to do what you did and have a serious conversation about it.
I understand that they'll do what they want anyhow, and that you can't watch them 24/7, but I guess I've always been mindful of the "you can make those type of decisions when you're an adult and start paying your way" more so than encouraging it. It's not saying I didn't sneak a beer, stay out late, go somewhere I wasn't supposed to be to see some chick, or whatever, but for the most part, my parents tried to push the decisions like alcohol, tobacco, sex and drugs are things you aren't old enough to make until you're out of the house. It's a twister, but I think I would stick with the, "I'm old enough to make these types of choices, and when you show me you're also at that stage, we can talk about it". But I don't think I would ever want it being a nightly, weekly, or frequent habit that a kid of mine smoked. At least not while they lived in my home. I guess a mature kid, I could see the side of letting them have one on a 'special occasion with dad', and as they turn 18, letting them into the fun in a larger basis. I just don't know that kids really comprehend the complexity of the choice, and have the respect for it that they should. It's not evil, and it's not a bad thing, but at the same time, like all good things, moderation is a practice I would want to encourage.
Good luck with it man, and I don't envy the conversations and tip toeing of a wife with it either. I can imagine what my mom would have done if she thought my dad got me hooked on things she didn't approve of.